Torque control device for air wrenches



March 25, 1969 'rz'rsuo MITANI ET AL 3,434,547

TORQUE CONTROL DEVICE FOR AIR WRENCHES Filed March 27, 1967 INVENTORS BYdazw, fla /97M.

ATTORNEYS United States Patent Office 3,434,547 Patented Mar. 25, 1969Int. Cl. B23q 5/ (l6; F15b 21/02 US. Cl. 173-1 1 Claim ABSTRACT OF THEDISCLOSURE A torque control device for a pneumatic wrench with apressure reducing valve for regulating the pressure of air to besupplied to the wrench, a change-over valve provided in a passage forthe air, and a timer adapted to actuate the changeover valve in responseto a pressure variation in the passage and to return the changeovervalve to its original position after expiration of a predeterminedperiod of time, so that the pneumatic wrench operates under a certainpressure of the air supplied for a predetermined period of time. Aspecific embodiment includes a ratchet-type switch inserted in theelectric circuit for energizing and de-energizing the changeover valve,which cooperates with the timer.

The present invention relates to a device for controlling the torque ofpneumatic wrenches such as the so-called impact wrench whereinrotational energy accumulated in a rotor is converted into impact energyby means of a ratchet mechanism so as to impart a torque to a drivenmember such as a screw.

In tightening a member, such as a screw, with a pneu matic wrench, ahighly complicated operation has heretofore been required involvingreadjustment of the tightening force by the use of a torque wrench,wherever the the tightening force is limited so as to fall within apredetermined range. In order to deal with such problem, various formsof pneumatic wrenchs have hitherto been proposed which are capable ofcontrolling the torque to be generated thereby to a desired valuebeforehand and thereby restricting the tightening force. However, sincemost of these conventional pneumatic wrenches are of the type having acontrol device accommodated therein, they are inevitably large andheavy. Consequently, these wrenches have the drawbacks that they areinconvenient in handling, complicated in construction and difiicult inmaintenance and adjustment, and further that they are only applicable torelatively small-sized screws. The same is more or less true with thepneumatic wrenches of the type having a control device attached on theexterior thereof. Namely, the wrenches of this type are generallycomplicated in construction, complicated in torque setting operation anddifficult to maintain.

According to the present invention, there is provided a torque controldevice which not only may be readily attached to the conventionalpneumatic wrenches but which is easy to maintain aind adjust. Further,this invention is capable of controlling the torque in a stable mannerand is effective in shortening the operating period of an associatedwrench and preventing wasteful consumption of the air used.

In order that the present invention may be more clearly understood,reference may now be had to the accompanying drawings in which thepresent invention is illustrated by way of example and in which:

FIG. 1 is a chart illustrating the operational characteristic curve of apneumatic wrench; and

FIG. 2 is a system diagram of an embodiment of the torque controldevice.

Referring to FIG. 1, there is shown the general relationship betweentorque T to be generated by a pneumatic wrench, and operating period Sof and pressure P supplied to the pneumatic wrench. As will be seen fromthis chart, a desired torque T may be obtained by restricting theoperating period of the pneumatic wrench to S at a pressure P oralternatively by restricting the pressure to P and operating the wrenchfor a period 5; or more. The former method is advantageous in shorteningthe operating period of the wrench but has the drawback that the torqueto be obtained is unstable, whereas the latter method has the advantagethat it is possible to obtain a relatively stable torque as a result ofoperation for a sufficiently prolonged period but on the other hand hasthe drawback that pressurized air used tends to be consumed wastefullyor a desired torque cannot be obtained if the operating period is notsufiiciently long. It will, therefore, be understood that, in order toobviate the foregoing drawbacks, both methods should be combined in asuitable manner. Namely, a desired stable torque T can be obtainedpositively and without waste of air and time by setting the supplypressure at P and also restricting the operating period to S Based onthis concept, the device of the present invention includes a pressurereducing valve for regulating the pressure of air supplied to anassociated pneumatic wrench and a change-over valve for shutting down apassage for said air to thereby stop the operation of the wrench after apredetermined lapse of time, said changeover valve being actuatedautomatically by means of a timer, whereby the pressure of the airsupplied to the wrench and the operating period of said wrench areregulated to desired values respectively, so as to control a torque tobe obtained.

FIG. 2 shows an embodiment of the inventive device using an electricaltimer. In this embodiment, a pneumatic system comprises a pressurereducing valve 1 for regulating the pressure of air under pressuresupplied from a pressurized air supply source SUT to an associatedpneumatic wrench 2 and an electromagnetically operative change-overswitch 3 interposed between said pressure reducing valve 1 and saidwrench 2 to change-over the supply passage from the former to thelatter. The inlet side and the outlet side of the change-over valve arecommunicated with each other through a throttling portion 4 and apressure difference produced between both sides of the throttlingportion 4 is utilized to actuate a switch actuator 5. The electricsystem, on the other hand, consists of a ratchet type switch 6 adaptedto be actuated by said switch actuator 5, a time switch 7 arranged to beopened in a predetermined period of time and a solenoid SOL to actuatethe aforementioned change-over valve 3. When the air wrench 2 is not inoperation, the main pressure supply passage leading from the pressurereducing valve 1 to the wrench 2 is closed by the change-over valve 3 asshown in the figure and, therefore, the pressures on the front and backsides of the throttling portion 4 are held in a balanced state. Theswitch actuator 5, therefore, is inoperative, holding the switch 6 in anopen position. Upon opening a valve provided in the wrench 2 to set saidair wrench in operation, the pressurized air present on the 'back sideof the throttling portion 4 is first consumed and thus a pressuredifference is developed between both sides of the throttling portion. Asa result, the switch actuator 5 is actuated by the pressure difference,bringing the switch 6 into a closed position, although the wrench 2 hasnot yet been set in motion under this state. Upon closing the switch 6,the solenoid SOL is energized to bring the change-over valve 3 into anopen position and thereby the wrench 2 is set in motion. The switch 6 iscontinuously held in the closed position even after the switch actuator5 is returned to its original position upon disappearance of thepressure ditference between both sides of the portion 4. Afterexpiration of a predetermined period of time, the time switch 7 isactuated to deenergize the solenoid SOL and the change-over valve 3 isclosed to stop the operation of the wrench 2. Upon closure of thechangeover valve 3-, as will be. understood, a pressure difference isdeveloped again between both sides of the throttling portion 4, so thatthe switch actuator 5 is again actuated thereby bringing the ratchettype switch 6 into the open position. By closing the valve in the wrench2, the pressure difference is eliminated, and the switch actuator 5 isreturned to its original position. Thus, the entire device is broughtinto the inoperative position completely in which said device had beenbefore the operation.

As will be understood from the foregoing description, since, accordingto the present invention, the torque generated by the pneumatic wrenchis controlled automatically by regulating the air pressure supplied tothe wrench and the duration of supplying it, the operator is onlyrequired to actuate the valve in the wrench and to hold it until theoperation is stopped automatically, there being no necessity forreadjustment of the tightening force by the use of a torque wrench orthe like as has been required with the conventional wrenches. With theinventive device,

therefore, it is possible to perform the tightening operation with easewhich has heretofore required a skill of the operator, and also toafford a uniform tightening strength to a part to be tightened asrequired. Consequently, it is possible to avoid excess or shortage oftightening force or wasteful consumption of the pressurized airresulting from an unduly prolonged operation of the wrench, which havebeen experienced even by those skilled in the tightening operation usingan impact wrench, as a result of difiiculty in determining the time ofcompletion of tightening. A still further advantage of the inventivedevice is that it may be readily attached to the air wrenches ofconventional forms and can be handled with ease.

We claim:

1. A torque control device for a pneumatic wrench,

comprising an air pressure reducing valve for regulating the pressure ofair supplied to said pneumatic wrench, a main air conduit between saidair pressure reducing valve and said pneumatic wrench,a'solenoid-operated changeover valve provided in said main air conduitfor opening and closing said conduit, a branch passage including thereina throttle valve in series, the up-stream end of said passage opening insaid main air conduit between said pressure reducing valve and saidchangeover valve and the down-stream end of said passage opening in saidmain air conduit at between said changeover valve-and said pneumaticwrench, a pneumatically-operated switch actuator actuated by thepressure difference created in said branch passage across said throttlevalve, an electric circuit for energizing the solenoid of saidchangeover valve, a timer switch provided in the circuit to open thecircuit at a predetermined time after said pneumatic wrench is caused tooperate by the opening of an operators valve of said wrench, and aratchet-type switch provided in said circuit and actuated by said switchactuator to close the circuit only when said switch actuator is actuatedby the opening of said operators valve in said pneumatic wrench and toopen said circuit only when said switch actuator is actuated when thetimer switch opens said electric circuit to close said changeover valvein said main air conduit.

References Cited UNITED STATES PATENTS 3,033,236 5/1962 Rayman et al.3,093,114 6/1963 Heidler 9138 X 3,195,655 7/1965 Karden 173-12 X3,336,840 8/1967 Alexander 173-12 X r ERNEST R. PURSER, PrimaryExaminer.

US. Cl. X.R. 9135; 137-62412

